Polyepoxide compositions containing dicyandiamide and an iodonium, phosphonium, or sulfonium salt

ABSTRACT

The disclosure of this application is directed to polyepoxide compositions, containing dicyandiamide and an iodonium, phosphonium or sulfonium salt, which are relatively stable at room temperature and can be cured at moderately elevated temperatures in a relatively short period of time to thermoset products characterized by excellent thermal stability, and when used in adhesive applications to bond together materials such as wood, plastic and metal, by excellent bonding strength.

United States Patent Sum [4 Sept. 12, 1972 POLYEPOXIDE COMPOSITIONS 3,377,406 4/1968 Newey et al ..260/837 CONTAINING DICYANDIAMIDE AND AN IODONIUM, PHOSPIIONIUM, OR SULFONIUM SALT Inventor: James J. Sura, Warren Township,

Assignee: Union Carbon Corporation Filed: March 2S, 1971 Appl. No.: 128,133

References Cited UNITED STATES PATENTS Dante et al. ..260/47 Primary Examiner-William H. Short Assistant ExaminerT. E. Pertilla Attorney-Paul A. Rose, Aldo J. Cozzi and James C. Arvantes 5 7] ABSTRACT The disclosure of this application is directed to polyepoxide compositions, containing dicyandiamide and an iodonium, phosphonium or sulfonium salt, which are relatively stable at room temperature and can be cured at moderately elevated temperatures in a relatively short period of time to therrnoset products characterized by excellent thermal stability, and when used in adhesive applications to bond together materials such as wood, plastic and metal, by excellent bonding strength.

13 Claims, No Drawings Zi /i980 Belanger ...26Q/47 POLYEPOXIDE COMPOSITIONS CONTAINING DICYANDIAMIDE AND AN IODONIUM, PI'IOSPHONIUM, OR SULFONIUM SALT and can be cured in a relatively short period of time by heating at moderately elevated temperatures, to thermoset products characterized by excellent thermal stability, and when used as adhesives to bond together materials such as wood, plastic, metal and the like, by excellent bonding strength.

Polyepoxide compositions are cured to thermoset products by admixing a curing agent therewith with the result that a reaction occurs between the reactive components of the composition and the composition cures to a thermoset product. This has presented a serious practical problem of utilizing these compositions inasmuch aspolyepoxide compositions, containing conventional curing agentssuch as tetraethylenetriamine usually cure to thermoset'products, even at ambient temperatures, in a relatively short period of time.

It has been suggested, therefore, that latent-act ing curing agents, such as dicyandiamide be employed with the polyepoxides to obtain compositions which are relatively stable at room temperature and consequently have relatively long storage or shelf life.

The use of dicyandiamide as a latent-acting curing agent for polyepoxide compositions has not proved to be particularly effective, however, especially when the resultant polyepoxide compositions are to be used as adhesives. It has been found necessary to heat these compositions to relatively high temperatures in order to effect a cure thereof. High temperature curing is highly undesirable as it excludes the use of these com positions as adhesives in the bonding of heat-sensitive materials.

The present invention provides polyepoxide compositions which are relatively stable at room temperature, that is have relatively long storage or shelf life and which can be cured at moderately elevated tempera tures, in a relatively short period of time, to thermoset products which are characterized by excellent thermal stability and when used as adhesives to bond together wood, metal, plastics and other like material, by excellent bonding strength.

The compositions of this invention comprise a polyepoxide, dicyandiamide and an iodonium, phosphonium or sulfonium salt wherein: the dicyandiamide is present in an amount sufficient to cure the polyepoxide to a thermoset product, generally in an amount of about 70 percent of stoichiometric to about 25 percent in excess of stoichiometric; and the iodonium, phosphonium or sulfonium salt is present in an amount of about 5 to about 50 percent by weight, preferably about 5 to about 40 percent by weight, based on the weight of the dicyandiamide.

For purposes of stoichiometric calculations with respect to the dicyandiamide, one hydrogen atom is deemed to react with one epoxy oxygen atom.

Illustrative of suitable polyepoxides for purposes of this invention are those organic compounds having an epoxy equivalency of greater than one, that is, comgroup, i.e., oxirane epoxy group, per molecule. These compounds wherein the oxygen of the epoxy group is attached to vicinal carbon atoms can be saturated or unsaturated, aliphatic, cycloaliphatic, or heterocyclic, and can be substituted, with substituents such as halogen atoms, hydroxyl groups, ether groups, and the like.

Among suitable polyepoxides are the polyglycidyl ethers of polyhydric phenols, exemplified by the polyglycidyl ethers of such phenols as the mononuclear polyhydric phenols, resorcinol and pyrogallol, the dior polynuclear phenols, such as the bisphenols described in Bender et al, U. S. Pat. No. 2,506,486, and polyphenylols such as the novolak condensation product of a phenol and a saturated or unsaturated aldehyde containing an average of'from 3 to 20 or more phenylol groups per molecule (cf. Phenoplasts by T. S. Carswell, published in 1947 by lnterscience Publishers, New York). Exemplary of suitable polyphenylols derived from a phenol and an unsaturated aldehyde such as acrolein are the triphenylols, pcntaphenylols, and heptaphenylols described in U. S.

Pat. No. 2,885,385 to A0. Farnham. The phenols may contain substituents such as alkyl or aryl ring substituents or halogens, as exemplified by thev alkyl resorcinols, tribromoresorcinol, and the diphenols containing alkyl and halogen substituents on the aromatic ring (Bender et al., U. S. Pat. No. 2,506,486). The polyhydric polynuclear phenols can consist of two or more phenols connected by such groups as methylene, alkylene, or sulfone. The connecting groups are further exemplified by bis(p-hydroxyphenyl)methane, bis(phydroxyphenyl)dimethylmethane, and dihydroxydiphenylsulfone.

Process for the preparation of polyglycidyl ethers of polyhydric phenols is described in detail in the Bender et al. patent, supra, and U. S. Pat. No. 2,801,989 to A. G. Farnham.

Among the more common polyglycidyl ethers of polyhydric phenols are polyglycidyl ether of 2,2-bis(phydroxyphenyl)-propane and polyglycidyl ether of bis(phydroxyphenyl)methane. Other suitable polyglycidyl ethers of polyhydric phenols are enumerated in US. Pat. No.2,633,458. i

Also suitable are the polyglycidyl ethers of polyhydric alcohols, such as the reaction products of epichlorohydrin and polyhydric alcohols for example, aliphatic compounds containing from two to four alcoholic hydroxyl groups, such as ethylene glycol, propane diols, butane diols, glycerine, hexane triols, and the like. (Methods of preparing polyglycidyl ethers of polyhydric alcohols are described in U. S. Pat. No. 2,898,349 to P. Zuppinger et al.)

Other suitable polyglycidyl compounds are the polyglycidyl esters of polycarboxylic acids, such as the polyglycidyl esters of adipic acid, phthalic acid, and the like. Polyglycidyl esters of polycarboxylic acids are described in detail in U. S. Pat. No. 2,870,170 to Payne et al. Also suitable are polyglycidyl compounds produced by reacting epichlorohydrin with aromatic amines, such as aniline, 2,6-dimethylaniline, ptoluidine, m-chloraniline, p-aminodiphenyl, m-phenylenediamine, p-phenylenediamine, 4,4- diaminodiphenylmethane, or with amino phenols such triglycidyl derivative of p-aminophenol wherein the amino hydrogen and OH hydrogen atoms are replaced by glycidyl groups. Polyglycidyl derivatives of aromatic amines and amino phenols and methods for their preparation are further described in U. S. Pat. No. 2,951,882 to N. H. Reinking and in U. S. Pat. No. 2,951,825 to N. H. Reinking et al. The so-called peracetic acid epoxides which are obtained by epoxidation across a double bond using peracetic acid, such as bis-(2,3-epoxycyclopentyl)ether and the like are also suitable.

It is to be understood that the disclosure of all patents and literature references referred to in this specification'are incorporated herein by reference.

Exemplary of phosphonium salts, used in the present invention are thephosphonium halides having "the formula:

FormulaI Wherein X is a halogen atom, chlorine, bromine, iodine or fluorine and each R-R, which can be the same or different, are hydrocarbon radicals, including hydrocarbon radicals substituted with one or more functional groups such as halogens, hydroxy and the like. Generally the hydrocarbon radicals have a maximum of 18 carbon atoms and preferably a maximum of carbon atoms.

Among suitable phosphonium halides are the following: methyl triphenyl phosphonium iodide, ethyl triphenyl phosphonium iodide, propyl triphenyl phosphonium iodide, n-butyl triphenyl phosphonium iodide, iso-butyl triphenyl. phosphonium iodide, secbutyl triphenyl phosphonium iodide, n-pentyl triphenyl phosphonium iodide, n-decyl triphenyl phosphonium iodide, methyl tri-n-butyl phosphonium iodide, ethyl tri-n-butyl phosphonium iodide, propyl tri-n-butyl phosphonium iodide, methyl triphenyl phosphonium chloride, ethyl triphenyl phosphonium chloride, isopropyl-tri-n-butyl phosphonium chloride, n-butyl triphenyl phosphonium chloride, ethyl triphenyl phosphonium bromide, ethyl triphenyl phosphonium fluoride and the like.

Suitable sulfonium salts, used in the present invening the formula:

Formula II wherein R-R and X are as defined in Formula I.

Specific sulfonium halides falling within the scope of Formula ll are: trimethyl sulfonium iodide, triethyl sulfonium iodide, methyl diethyl sulfonium iodide, ethyldi-n-propyl sulfonium iodide, tri-B-hydroxyethyl sulfonium chloride, triphenyl sulfonium iodide and the like.

lodonium salts, suitable for purposes of this invention are the iodonium halides having the formula:

Formula 111 i I [Xl' Iii Wherein R, R and X are as defined in Formula I.

Suitable sulfonium halides fallingwithin the scope of Formula 111 are: diphenyl iodonium iodide, diphenyl iodonium chloride and the like.

Other suitablesalts are described in US. Pat. Nos. 3,477,990 and 3,412,046.

It is to be noted that mixtures of iodonium, phosphonium and sulfonium salts can be used if so desired.

The compositions of this invention are prepared by admixing the polyepoxide, dicyandiamide and the salts" together at room temperature in any suitable vessel or if desired, on a three roll mill.

Curing of these compositions can be effected at moderately elevated temperatures generally on the order of about 250 F. to about 350 F. and preferably about 275 F. to about 300 F.

Additional materials such as fillers, pigments, fibers, dyes, plasticizers and the like can be added to the compositions of the present invention, if so desired.

In the following examples, which are illustrative of the present invention, the compositions were formulated on a three roll mill and used as adhesives to bond together, in each case, two aluminum panels by coating one of the panels to a thickness of 2 mils and then pressing the two aluminum panels together. The panels were then subjected to heat and pressure. The bonding strength of each composition was determined by the Lap Shear Strength test. (ASTMDl002-64) The curing cycles used are set forth in the tables below. Also set forth in the tables below, along with the result of the Lap Shear Strength test are the formulations of the compositions wherein amounts noted are in tion, include among others the sulfonium halides havparts by weight.

TABLE I Examples Controls Triglycidyl derivative of p-aminophenoL 100 100 100 100 100 100 10 Asbestos.- u 30 30 30 30 30 30 30 30 Dicyandiamide 18. 6 18. 6 13. 6 18. 6 18. 6 18.6 18. 6 18. 6 Ethyl triphenyl phosphonium iodide 2. 5 4. 0 Diphenyl iodonium iodide 2. 5 4. 0 Trimethyl sulfonium iodide .t 1 2. 5 4. 0 Tetramethyl ammonium iodide 2. 5 4. 0 Lap shear strength, cured hour at 250 F. under a pressure of 100 tested .it

TABLE ll Exmuplus T k it ill ll (nllh'ol 3 Diglycldylether of 2,2-bis-(p-hydroxyphenyl) propane 100 100 100 100 mu \uu Asbestos s s 3U 3U 30 30 30 30 Dlcyandlamlde 10 l l0 10 ll) Ethyl triphenyl phosphonlurn lodid Diphenyl iodonium iodide 'Irimethyl snlfoniuml dide n n.1,... Lap shear strength, cured 30 minutes at 275 F. under a pressure of 100 p.s.i., tested at: 73 F 2, 784 3,132 l, 700 2, 4x0 2, 232 0 Nora-The diglycldylether had an epoxy equivalent weight of 190.

Tests were also conducted as to the stability of the 5. A curable composition as defined in claim 1 compositions. Compositions tested and the results wherein the polyepoxide is the diglycidylether of 2,2- thereof are noted below. bis-(p-hydroxyphenyl)propane.

' 6. A curable composition as defined in claim 1 Compositions Gel Time wherein the said salt has the formula: Example 1 did not gel after 4 months at ambient temperatures R R1 H Example 2 Example 3 /P\ [X] Example 4 R, R, Example 5 v I Example 6 wherein X is a halogen atom, and R-R are monovalent Control 1 gelled after one month at hydrocarbon radicals containing a maximum of 18 carambient IBITIPCX'BUICS bon atoms.

7. A curable composition as defined in claim 1 wherein the said salt has the formula:

Control 4 Control 4 was the same as Control 1 with the excep- R H tlon that tetramethyl ammonium chloride was used in l RL-S IX!- lieu of the tetramethyl ammonium iodide. I

What is claimed is 1. A curable composition consisting essentially of a polyepoxide having an epoxy equivalency of more than wherem R412 and x are as defined m clam one wherein the oxygen of each epoxy group is atcurable as defined l tached to vicinal carbon atoms, dicyandiamide in an wherein the said salt 15 tnmethyl sulfomum iodide. amount sufficient to cure said composition to a ther- A curable composmon as defined m clam 1 moset product and aphosphonium or sulfonium salt in the Said salt is ethyl triphenyl phosphonium an amount of about 5 to about 50 percent by weight, Iodide based on the weight ofthe dicyandiamide 10. A curable compos tion as defined in claim 8 A curable composition as defined in claim 1 wherein the polyepoxide 1s dlglycidylether of 2,2-biswherein the dicyandiamide is present in an amount of (p'hydroxy'phenyl)pmpane' about 70 percent of stoichiometric to about 25 percent 40 A curable Composmon as defined in Claim 9 in excess of stoichiomemm wherein the polyepoxide is diglycidyl ether of 2,2-bis- 3. A curable composition as defined in claim 1 (phydroxyphenyl)pmpanf, f d l 1 wherein the said salt is present in an amount of about 5 curable comPosmPn me m c am to about 40 percent by weight, based on the weight of T' the pdyepoxlde mglyc'dyl ether of the dicyandi ide. amlnophenol.

4. A cura le composition as defined in claim 1 13. The cured product of the composition defined 111 wherein the polyepoxide is a polyglycidylether of a Claim polyhydric phenol. t e a: e 

2. A curable composition as defined in claim 1 wherein the dicyandiamide is present in an amount of about 70 percent of stoichiometric to about 25 percent in excess of stoichiometric.
 3. A curable composition as defined in claim 1 wherein the said salt is present in an amount of about 5 to about 40 percent by weight, based on the weight of the dicyandiamide.
 4. A curable composition as defined in claim 1 wherein the polyepoxide is a polyglycidylether of a polyhydric phenol.
 5. A curable composition as defined in claim 1 wherein the polyepoxide is the diglycidylether of 2,2-bis-(p-hydroxyphenyl)propane.
 6. A curable composition as defined in claim 1 wherein the said salt has the formula:
 7. A curable composition as defined in claim 1 wherein the said salt has the formula:
 8. A curable composition as defined in claim 1 wherein the said salt is trimethyl sulfonium iodide.
 9. A curable composition as defined in claim 1 wherein the said salt is ethyl triphenyl phosphonium iodide.
 10. A curable composition as defined in claim 8 wherein the polyepoxide is diglycidylether of 2,2-bis-(p-hydroxy-phenyl)propane.
 11. A curable composition as defined in claim 9 wherein the polyepoxide is diglycidyl ether of 2,2-bis-(p-hydroxyphenyl)propane.
 12. A curable composition as defined in claim 1 wherein the polyepoxide is triglycidyl ether of p-aminophenol.
 13. The cured product of the composition defined in claim
 2. 